1. Field of the Invention
The present invention relates to a radio wave reception converter (LNB: Low Noise Block down Converter) receiving radio waves such as those of satellite broadcasting and converting the radio wave into an electric signal, and an antenna apparatus including such a radio wave reception converter.
2. Description of the Background Art
FIG. 7 is a sectional view of a structure of a conventional radio wave reception converter.
As shown in FIG. 7, the conventional radio wave reception converter has a horn 102 secured by a screw 109a to a chassis main unit 101 having a waveguide 110. Connection between horn 102 arid an exterior cabinet 105 is established by attaching a nut 124 to the screw portion of an output terminal 108 provided at chassis main unit 101. Accordingly, exterior cabinet 105 is urged against and secured to horn 102: At the front of horn 102, a feedome 104 (also called horn cap) is secured by a screw 109b. 
An O ring 111 is located at the connection between horn 102 and exterior cabinet 105. Additionally, an O ring 113 is located at the connection between exterior cabinet 105 and output terminal 108. These O rings function to establish hermetic sealing of the interior of exterior cabinet 105 against outside air. Furthermore, an O ring 112 is located at the connection between feedome 104 and horn 102. This O ring functions to establish hermetic sealing of the interior of horn 102 and the interior of waveguide 110 against outside air.
FIG. 8 is a sectional view of a structure of another conventional radio wave reception converter.
As shown in FIG. 8, this another conventional radio wave reception converter has a horn 202 press-fitted and secured at the front end of a waveguide 210 formed of a cylindrical metal pipe. At the rear of waveguide 210, a circuit board 207 having a converter circuit formed is attached. Waveguide 210, horn 202 and circuit board 207 are covered with bisected exterior cabinets 205a, 205b and feedome 204. Connection of the bisected exterior cabinets 205a and 205b is established through press-fitting or adhesion-fixing. Additionally, connection between exterior cabinet 205a and feedome 204 is established by press-fitting or adhesion-fixing. Thus, the interior of the radio wave reception converter is maintained in an airtight manner.
The structure of other conventional radio wave reception converters is disclosed in, for example, Japanese Utility Model Laying-Open No. 64-5501, Japanese Utility Model Laying-Open No. 64-15410, Japanese Patent Laying-Open No. 2-75226, Japanese Utility Model Laying-Open No. 62-100710, Japanese Utility Model. Laying-Open No. 4-57927, and the like.
The radio wave reception converter of the structure shown in FIG. 7 has the problem that extremely strict accuracy is required in the surface roughness of respective faces of feedome 104, horn 102, exterior cabinet 105 and the like brought into contact with O rings 111–113 as well as the dimension of the groove in which O rings 111–113 are fitted since airtightness is ensured by O rings 111–113. If the accuracy of such elements are not maintained at a high level, moist air will flow into the radio wave reception converter to significantly degrade the product lifetime. It is therefore necessary to realize the high accuracy set forth above, imposing constraints on the fabrication cost.
The radio wave reception converter of the structure shown in FIG. 8 is absent of O rings, and maintains airtightness by press-fitting or adhesion-fixing. This imposes the problem that strict dimension accuracy is required. However, exterior cabinets 205a and 205b as well as feedome 204 are generally resin-formed components, relatively harder to achieve critical dimension accuracy as compared to metal. Therefore, when the press-fitting process is employed, airtightness of a level that can prevent intrusion of rain can be ensured. However, it is extremely difficult to prevent intrusion of moist air. In the case where adhesion-fixing is employed, the working process becomes tedious since the adhesive must be applied evenly over the entire face of connection. Furthermore, overflow of the adhesion will become the cause of deterioration in appearance.